Fix optimistic state not being replaced by server data in writeInsert

Fixes #814

When writeInsert() is called from within an onInsert handler, the
transaction is in 'persisting' state. Previously, commitPendingTransactions()
would re-apply optimistic state from persisting transactions after syncing
server data, causing server-generated fields to be overwritten with
optimistic client-side values.

This fix excludes 'persisting' transactions from having their optimistic
state re-applied during commitPendingTransactions(). This ensures that
when writeInsert() syncs server data (e.g., server-generated IDs), that
data is not immediately overwritten by the optimistic state.

The flow now works correctly:
1. User inserts item with temporary ID -> optimistic state shows temp ID
2. Transaction commits -> onInsert handler called (state = 'persisting')
3. Handler calls writeInsert(serverItem) with real ID
4. commitPendingTransactions() syncs server data
5. Optimistic state from persisting transaction is NOT re-applied
6. UI now shows server data with real ID
7. Transaction completes -> optimistic state is cleared

Author: claude

packages/db/src/collection/state.ts

@@ -668,7 +668,7 @@ export class CollectionStateManager<
       // Always overlay any still-active optimistic transactions so mutations that started
       // after the truncate snapshot are preserved.
       for (const transaction of this.transactions.values()) {
-        if (![`completed`, `failed`].includes(transaction.state)) {
+        if (![`completed`, `failed`, `persisting`].includes(transaction.state)) {
           for (const mutation of transaction.mutations) {
             if (
               this.isThisCollection(mutation.collection) &&